Field of the Invention
This invention relates to a process for recovering useable products from the waste of phosphating systems. Particularly, the recovered products are capable of use as make-up feed in a zinc phosphating process. More particularly, this invention relates to a process of treating zinc phosphating system sludge with phosphoric acid to precipitate iron phosphate and allow recovery of a useable zinc phosphate solution.
The process of the invention is particularly well suited for use as a continuous process of removing sludge waste from a zinc phosphating operation, dissolving the sludge in water and phosphoric acid, precipitating iron phosphate from the solution, removing the iron phosphate precipitate and recycling the resultant zinc phosphate solution to the zinc phosphating operation as a make-up feed.
Throughout the specification, numerous references will be made to the use of sludge from a zinc phosphating process. However, it should be realized that the invention could be used in the treatment of any sludges containing iron and zinc phosphates. For example, nickel plating waste and carbon steel flue dust are treatable by this process to recover valuable products.